Ovalicin is a metabolite of Pseudorotium ovalis possessing antibiotic, antitumor, immunosuppressive, and seed germination stimulating properties. Fomannosin is a phytotoxic metabolite of the economically important wood-rot fungus Fomes annosus. The structure of each of these sesquiterpenes presents a unique and complex biosynthesis problem, not readily amenable to traditional radioisotopic labelling and degradation techniques. The proposed research intends to examine the application of a powerful new instrumental technique, carbon magnetic resonance, to the solution of the biosynthetic problems posed by these substances. The goal is 1) to elucidate the rearrangement pathway by which ovalicin is formed; 2) to establish a biosynthetic scheme for the formation of fomannosin and to provide mechanistic and stereochemical detail bearing on that scheme; and 3) to probe and extend the utility of homo- and heteronuclear double labelling in CMR studies of isoprenoid biosynthesis.